The present invention relates to a leak detector for detecting leaks in an oil/fuel heat exchanger in an aircraft turbojet engine lubricating circuit, more particularly such a detector which relies upon an increase of pressure in the oil reservoir caused by fuel mixing with the lubricating oil.
It is conventional practice in aircraft turbojet engines to provide lubricating oil for lubricating various rotating element of the turbojet engine and to cool the lubricating oil by passing it through a fuel/oil heat exchanger which is also connected to the fuel supplied to the engine. The turbojet engine components to be lubricated, such as the turbine bearings, are mounted in an enclosure having a vent hole to establish a reference pressure within the enclosure. A supply pump feeds the lubricating oil from a lubricating oil reservoir through a supply conduit to a spray device located in the enclosure which sprays the oil onto the elements to be lubricated. The lubricating oil circuit may include a return pump which returns the used lubricating oil to the reservoir. Also, an oil filter may be inserted into the return conduit downstream of the return pump. The oil/fuel heat exchanger is typically located between the oil filter and the lubricating oil reservoir.
In order to maintain a slightly excess pressure inside the lubricating oil reservoir, a pressure balancing conduit connects the reservoir to the lubricating enclosure. To compensate for imbalances between the flows of the supply pump and the return pump, the balancing conduit allows air to freely transfer between the oil reservoir and the lubricating enclosure such that the pressure in the reservoir will be substantially equal to the reference pressure in the lubricating enclosure.
Aircraft procedures during aircraft flight require the stopping of the turbojet engine if there is a lubricating circuit malfunction. Means are provided to measure the pressure differential between the outlet pressure of the supply pump and the reference pressure within the lubricating enclosure. When this pressure differential becomes less than a predetermined value, an alarm is transmitted to the aircraft pilot so that he may take the appropriate action.
The pressure of the fuel circulating through the heat exchanger is significantly higher than the outlet pressure of the return pump for the lubricating oil. In case of a malfunction or a leak between the two fluid circuits in the heat exchanger, fuel will be introduced into the lubricating circuit due to its higher pressure. The oil diluted by fuel will seriously degrade the engine components and presents the danger of engine fires, especially when the engine has stopped after the aircraft is on the ground. Under these circumstances, the air/oil labyrinth seals of many engine parts lose their effectiveness, which may allow an oil/fuel mixture to come into contact with high temperature engine components.